The invention relates generally to linear synchronous motors and more particularly to a linear synchronous motor having variable pole pitches generating propulsion and levitation forces for a high speed transportation system.
The concept of using superconducting magnets for a magnetic levitation transportation system has been developed and proven to work in the United States. An alternating--current (AC) magnetic repulsion system was first conceived by Emile Bachlelet, a French engineer working in the U.S. He built a model vehicle in 1912 using magnetic forces for levitation and repulsion. Bachlet's concept law dormant until the mid-1960's when James Powell and Gordon Danby, both from Brookhaven National Laboratory, proposed that superconducting magnets in combination with linear synchronous motors could make the concept practical. (Powell, J. R., and Danby, G. R., 1967, A 300-mph Magnetically Suspended Train, Mechanical Engineering, 89:30-35, November; U.S. Pat. No. 3,470,828) From their concepts their invention of the low-drag, null-flux guideway using discrete coils followed, an approach that is still viable and a variant of which is being used in Japan.
Several methods have been proposed for propelling magnetic levitation (Maglev) vehicles. The most compatible appears to be the long stator/guideway linear synchronous motor. This concept uses a stator winding in the form of a guideway that is supplied with three-phase AC power and energized sequentially, causing a magnetic wave to travel along the guideway. This traveling magnetic wave interacts with the vehicle-borne superconductive coils to propel the vehicle.
In 1986 a linear synchronous unipolar motor of original construction was developed at Boeing Aerospace, as disclosed in Gilliland, R. G., D. D. Lyttle, and G. W. Pearson, Integrated Magnetic Propulsion and Suspension, Final Report, prepared by Boeing Aerospace Co., for U.S. Dept. of Transportation, Urban Mass Transportation Administration Report UMTA-WA-06-0014-086-2, December, 1986.
The latest review of the Maglev technology is fully reflected in the report of Argonne National Laboratory, "Maglev Vehicles and Superconductor Technology: Integration of High Speed Ground Transportation into the Air Travel System" (Available from the National Technical Information Services, US Department of Commerce, 5285 Port Royal Road, Springfield, Va. 22161).
The construction of the linear synchronous motors that have been presented so far have the following limitations:
1. To start up and accelerate its moving part, the linear motor needs to be supplied with a special generator having currents of varying frequency that smoothly increase according to the vehicle's desired acceleration/deceleration;
2. The recovery of energy when the vehicle is decelerating is impeded and thus will not occur;
3. The power factor of known linear synchronous motors is very low;
4. If superconductivity failure occurs, a severe accident may result;
5. To create the capacity for levitation, it is necessary to introduce a special winding on the stator that results in the waste of additional energy; and
6. To shield the magnetic field of the superconductive magnets, which is dangerous to human health, a considerable increase in the vehicle's weight and dimensions is required.
In view of the prior art, there is a need for a linear synchronous motor that overcomes the above-mentioned limitations.